Carboxylic acids are weak acids and dissociate in an aqueous solution to the carboxylate anion.   RCOOH(aq)↽−−⇀RCOO−(aq)+H+(aq) (Arrow is Reversible)    The extent of dissociation is given by the equilibrium dissociation constant, Ka, which is often expressed in its logarithmic form as pKa. (The cation is written simply as H+ and is understood to be solvated with one or more water molecules in solution.)   ?a=[H+][RCOO−]/[RCOOH]     pKa=−log(Ka)   If a formic acid in formate buffer is 0.022 M in formic acid and has a pH of 3.85, what is the molar concentration of the formate ion? The pKa of formic acid is 3.75.

The reaction just described is reversible. Deprotonation of the conjugate acid of an organic base by water provides another example of simultaneous making and breaking of sigma bonds. Thus, in the deprotonation of anilinium ion by water, the base is water, which has unshared electrons on the ________ atom. The acid is ________ ion. A pair of ________ electrons on the oxygen atom of water is pushed toward the ________ atom. Simultaneously, the pair of ________ electrons between the hydrogen and ________ atom of the anilinium ion is pushed toward the ________ atom. Thus, the oxygen- ________ sigma bond is made and a hydrogen- ________ sigma bond is broken. The nitrogen atom, which possessed a positive charge, is now ________, and the oxygen atom, which was neutral, now possesses a formal ________ charge.

Write the chemical equation and the expression for the equilibrium constant, and calculate Kb for the reaction of each of the following ions as a base. (a) sulfate ion (b) citrate ion

For conjugate acidbase pairs, how are Ka and Kb related? Consider the reaction of acetic acid in water CH3CO2H(aq)+H2O(l)CH3CO2(aq)+H3O+(aq) where Ka = 1.8 105 a. Which two bases are competing for the proton? b. Which is the stronger base? c. In light of your answer to part b. why do we classify the acetate ion (CH3CO2) as a weak base? Use an appropriate reaction to justify your answer. In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH3 is a weak acid. To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming Ka for a monoprotic strong acid is 1 106, calculate Kb for the conjugate base of this strong acid. Why do conjugate bases of strong acids have no basic properties in water? List the conjugate bases of the six common strong acids. To tie it all together, some instructors have students think of Li+, K+, Rb+, Cs+, Ca2+, Sr2+, and Ba2+ as the conjugate acids of the strong bases LiOH, KOH. RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acidic properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a_____base. The conjugate acid of a weak base is a_____acid. The conjugate base of a strong acid is a_____base. The conjugate acid of a strong base is a_____ acid. (Hint: Weak gives you weak and strong gives you worthless.)